Power light emitting diode and method with current density operation

ABSTRACT

A light emitting diode device emitting at a wavelength of 390-415 nm has a bulk gallium and nitrogen containing substrate with an active region. The device has a current density of greater than about 175 Amps/cm 2  and an external quantum efficiency with a roll off of less than about 5% absolute efficiency.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Ser. No. 61/243,988, filed Sep.18, 2009, commonly assigned, and hereby incorporated by referenceherein.

BACKGROUND OF THE INVENTION

This invention relates generally to lighting techniques, and inparticular to techniques for high current density LED devices fabricatedon bulk gallium and nitrogen containing polar, semipolar or nonpolarmaterials. The invention can be applied to applications such as whitelighting, multi-colored lighting, lighting for flat panel displays,other optoelectronic devices, and similar products.

In the late 1800's, Thomas Edison invented the light bulb. Theconventional light bulb, commonly called the “Edison bulb,” has beenused for over one hundred years. The conventional light bulb uses atungsten filament enclosed in a glass bulb sealed in a base, which isscrewed into a socket. The socket is coupled to AC power or DC power.The conventional light bulb can be found in houses, buildings, andoutdoor lighting, as well as in other areas requiring light.Unfortunately, more than 90% of the energy used for the conventionallight bulb dissipates as thermal energy. Additionally, the conventionallight bulb routinely fails often due to thermal expansion andcontraction of the filament element.

Fluorescent lighting overcomes some of the drawbacks of the conventionallight bulb. Fluorescent lighting uses an optically clear tube structurefilled with a noble gas and mercury. A pair of electrodes is coupledbetween the halogen gas and couples to an alternating power sourcethrough a ballast. Once the gas has been excited, the resulting mercuryvapor discharges to emit UV light. Usually the tube is coated withphosphors excitable by the UV emission to make white light. Manybuilding structures use fluorescent lighting and, more recently,fluorescent lighting has been fitted onto a base structure, whichcouples into a standard socket.

Solid state lighting techniques are also known. Solid state lightingrelies upon semiconductor materials to produce light emitting diodes,commonly called LEDs. At first, red LEDs were demonstrated andintroduced into commerce. Red LEDs use Aluminum Indium Gallium Phosphideor AlInGaP semiconductor materials. Most recently, Shuji Nakamurapioneered the use of InGaN materials to produce LEDs emitting light inthe blue color range for blue emitting LEDs. The blue colored LEDs leadto innovations such as state white lighting, and other developments.Other colored LEDs have also been proposed, although limitations stillexist with solid state lighting. Further details of such limitations aredescribed throughout the present specification and more particularlybelow.

A challenge for solid state lighting in the high cost of LED-basedlighting. Cost often is directly proportional to the semiconductormaterial real estate used to produce a given amount of light. To reducecost, more lumens must be generated per unit area of semiconductormaterial. Conventional InGaN LEDs, however, suffer from efficiency“droop” where internal quantum efficiency reduces as current density isincreased. The current density for maximum efficiency, Jmax, istypically 1-10 A/cm² which is a very low current density. Also, athigher power densities, current crowding and thermal gradients canresult in poor performance and reliability issues. These phenomena makeit difficult to reduce cost by increasing current density, as a minimumefficiency is necessary to provide energy savings for LEDs aboveconventional approaches like fluorescent and incandescent lighting.These and other limitations are described in further detail throughoutthe present specification and more particularly below.

From the above, it is seen that techniques tor improving optical devicesis highly desired.

BRIEF SUMMARY OF THE INVENTION

According to the present invention, techniques related generally tolighting are provided. Specifically, techniques for generating increasedlight output per unit area of GaN-based semiconductor material aredescribed. More specifically, embodiments of the invention include highcurrent density LED devices, with high active area utilisation (i.e.,ratio of active region area to dicing pitch), fabricated on bulk galliumand nitrogen containing polar, semipolar or nonpolar materials.

Conventional GaN-based LEDs are fabricated by epitaxial growth of devicelayers on foreign substrates, such as sapphire, Silicon Carbide (SiC),or Silicon (Si). In the case of sapphire, a lateral injection geometryis mandated due to the electrically insulating properties of sapphire.The lateral geometry may be top-emitting, through semi-transparent ohmiccontact metallization, or bottom-emitting (i.e., “Flip-Chip, or FCgeometry). Otherwise, the sapphire substrate may be removed, and athin-film approach employed, wherein the epitaxial device layers aretransferred onto a carrier substrate or package element. For Si, highlight extraction efficiency requires that the Si substrate be removed,mandating a dun-film approach. For SiC, either a lateral or thin-filmapproach is feasible.

For a fixed light output level, the main lever for reducing cost is bydecreasing the LED semiconductor area required for the lighting product.Reducing the total LED chip area effectively increases semiconductormanufacturing plant output, while reducing the size of optics and othercomponents used in final product assembly. Reducing chip size increasescurrent density, but high external quantum efficiency may be maintainedat high current density using epitaxial techniques of the presentinvention described below. Chip design also plays a critical role. Chipsize reduction for lateral chips (either top or substrate emitting) isproblematic as fabrication tolerances can reduce active area utilizationas chip size is reduced.

This effect is illustrated in FIG. 1. Lateral-injection devices (whethertop or bottom contacted) require area for making both anode and cathodeconnections on the same side of the device. This fundamentally reducesactive area utilization (portions of the die footprint are required forthe cathode) and puts a practical limit on die size. Assuminglithography tolerances of 5 um, a die-attach tolerance of 25 um, and abump diameter of 75 um, the active area utilization vs. chip width is asshown in the Figure. For SiC, a conductive buffer layer approach allowsthe use of a vertical injection design. However, the lattice mismatchbetween SiC and GaN results in high dislocation densities (>1×10⁸ cm-²)which can cause unreliability at high power densities. Also, SiC has ahigher refractive index than GaN, making the issue of light extraction amore difficult problem.

This invention provides a light emitting diode which includes a bulkgallium and nitrogen containing substrate with a surface region. One ormore active regions are formed overlying the surface region, with acurrent density of greater than about 175 Amps/cm² characterizing theone or more active regions. The device has an external quantumefficiency (EQE) of 40% (or 50%, 60%, 70%, 80%, 90%) and greater.

In an alternative embodiment, the invention provides an alternative typelight emitting diode device, but which also includes a bulk gallium andnitrogen containing substrate and one or more active regions formedoverlying the surface region. The device also has a current density ofgreater than about 200 A/cm² characterizing the active regions, and anemission characterized by a wavelength of 385-480 nm. In a specificembodiment, the device has desired red, green, blue, or other emittingphosphor materials operably coupled to the primary device emission toprovide a white light source.

In another embodiment, the invention provides a light emitting diodedevice with a bulk gallium and nitrogen containing substrate having anon-polar orientation. The device also has active regions formedoverlying the surface region and a current density of greater than about500 A/cm² characterising the active regions. The device has an emissioncharacterized by a wavelength of 385-415 nm and one or more RGB or othercolor phosphor materials operably coupled to the emission to provide awhite light source. In a further specific embodiment, the device has acurrent density of greater than about 500 A/cm² characterizing theactive regions and an emission characterised by a wavelength of 385-425nm.

In further embodiments, the invention provides a method of operating alight emitting diode device of the type described above. The methodsubjects the optical device to an electrical current such that ajunction region of the active regions provides a current density ofgreater than about 200 Amps/cm² and outputs electromagnetic radiationhaving wavelengths between 385-480 nm. The device preferably includes apackage enclosing at least the bulk gallium and nitrogen containingsubstrate and active regions. Preferably, the package is characterisedby a thermal resistance of 15 or 10 or 5 or 1 degrees per Watt and less.

In another embodiment the light emitting diode device has a currentdensity of greater than about 175 Amps/cm² characterizing the one ormore active regions. Additionally, the device has an internal quantumefficiency (IQE) of at least 50%; and a lifetime of at least about 5000hours operable at the current density.

Still further, the invention provides a method for manufacturing a lightemitting diode device. The method includes providing a bulk gallium andnitrogen containing substrate having a surface region and forming firstepitaxial material over the surface region. The device also includes oneor more active regions formed overlying the epitaxial materialpreferably configured for a current density of greater than about 175Amps/cm². The method can also include forming second epitaxial materialoverlying the active regions and forming contact regions.

The present invention provides an LED optical device with an active areautilization characterizing the active area which is greater than 50%. Inother embodiments, the utilisation is >80%, >90%, or >95%. Also theinvention enables a device with a ratio characterising the emittingouter surface area to active region area of greater than 1, and in otherembodiments, the ratio is >5, >10, or >100.

Still further, the present invention provides an apparatus, e.g., lightbulb or fixture. The apparatus has one or more LEDs having a cumulativedie surface area of less than about 1 mm² and configured to emit atleast 300 lumens. In a specific embodiment, the LEDs consists of asingle LED fabricated from a gallium and nitrogen containing materialhaving a semipolar polar, or non-polar orientation. If more than one LEDis provided they are preferably configured in an array.

Typically, the LED has an active junction area of a size with an activejunction area of less than about 1 mm² is less than about 0.75 mm², isless than about 0.5 mm², is less than about 0.3 mm². In a specificembodiment, the apparatus emits at least 300 lumens, at least 500lumens, or at least 700 lumens. In a specific embodiment, the emissionis substantially white light or in ranges of 390-415 nm, 415-440 nm,440-470 nm, and others. In other embodiments, the LED is characterizedby an input power per active junction area of greater than 2 watts/mm²,of greater than 3 watts/mm², of greater than 5 watts/mm², of greaterthan 1.0 watts/mm², of greater than 15 watts/mm², of greater than 20watts/mm², or others. Depending upon the embodiment, the LED ischaracterized by a lumens per active junction area of greater than 300lm/mm² for a warm white emission with a CCT of less than about 5000K andCRI of greater than about 75. Alternatively, the LED is characterized bya lumens per active junction area of greater than 400 lm/mm² for a warmwhite emission with a CCT of greater than about 5000K and CRI of greaterthan about 75. Alternatively, the LEDs is characterized by a lumens peractive junction area of greater than 600 lm/mm² for a warm whiteemission with a CCT of greater than about 5000K and CRI of greater thanabout 75. Alternatively, the LEDs is characterized by a lumens peractive junction area of greater than 800 lm/mm² for a warm whiteemission with a CCT of greater than about 5000K and CRI of greater thanabout 75.

The LEDs described herein can have a current density of greater thanabout 175 Amps/cm² characterizing the active regions and an externalquantum efficiency characterized by a roll off of less than about 5% inabsolute efficiency, as measured from a maximum value compared to thevalue at a predetermined increased operating current density, and anemission characterized by a wavelength of 390-480 nm.

The present LED is operable at a junction temperature greater than 100C, greater than 150 C, and/or greater than 200 C, and even higher. Inpreferred embodiments, the present device is operable in un-cooled stateand under continuous wave operation. The present LED device also has acurrent density that may range from about 175 A/cm² to about 1 kA/cm² ormore. In one or more preferred embodiments, the current density is alsoabout 400 A/cm² to 800 A/cm².

The device and method herein provide for higher yields over conventionaltechniques in fabricating LEDs. In other embodiments, the present methodand resulting structure are easier to form using conventional techniquesand gallium and nitrogen containing substrate materials having polar,non-polar or semipolar surface orientations. The present inventionprovides a resulting device and method for high current density LEDdevices having smaller feature sizes and substantially no “Droop.” In apreferred embodiment, the device provides a resulting white lightfixture that uses substantially reduced LED semiconductor area, ascompared to conventional devices. In a preferred embodiment, the presentLED active region designs are configured for reducing droop, enablingchip architectures that operate efficiently at high current densities.

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the specification and attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified illustration of chip size for (a) lateralinjection (e.g., flip-chip shown), (b) vertical thin-film, and (c)bulk-substrate based LEDs according to embodiments of the presentinvention.

FIG. 2 illustrates active area utilisation (ratio of active area todevice footprint) as a function of chip width for lateral chip designscompared with the present invention, assuming lithography tolerances of5 um, a die-attach tolerance of 25 um, and a bump diameter of 75 um.

FIG. 3 shows a sample plot of relative luminous flux as a function ofinjection current for a conventional LED, a Cree XP-E white LED withjunction temperature of 25° C.

FIG. 4 shows an external quantum efficiency as a function of currentdensity for (a) a multiple quantum well LED with two 2.5 nanometerwells, (b) a multiple quantum well LED with six 2.5 nanometer quantumwells, and (c) a double heterostructure LED with a 13 nanometer activeregion. Each of the LEDs exhibited emission at ˜430 nm.

FIG. 4A illustrates quantum efficiency plotted against current densityfor LED devices according to an embodiment of the present invention.

FIG. 5 is a simplified diagram of a high current density epitaxiallygrown LED structure according to an embodiment of the present invention.

FIG. 5A is a simplified flow diagram of an epitaxial deposition processaccording to one or more embodiments of the present invention.

FIG. 6 is a simplified diagram illustrating a high current density LEDstructure with electrical connections according to an embodiment of thepresent invention.

FIG. 7 is a simplified diagram of a bottom-emitting lateral conductinghigh current density LED device according to an embodiment of thepresent invention.

FIG. 8 is a simplified diagram of a bottom-emitting verticallyconducting high current density LED according to a specific embodimentof the present invention.

FIG. 9 is a simplified example of a packaged white LED containing a highcurrent density LED device according to an embodiment of the presentinvention.

FIG. 10 is a simplified diagram showing pulsed output power vs. currentdensity and external quantum efficiency vs. current density for an LEDfabricated on nonpolar GaN with an mission wavelength of ˜405 nmaccording to one or more embodiments.

FIGS. 11-15 are experimental results for LED devices according toembodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates generally to lighting techniques, and inparticular to techniques for high current density LED devices fabricatedon bulk gallium and nitrogen containing polar, semipolar or nonpolarmaterials. The invention can be applied to applications such as whitelighting, multi-colored lighting, lighting for flat panel displays,other optoelectronic devices, and similar products.

We have discovered that recent breakthroughs in the field of GaN-basedoptoelectronics have demonstrated the great potential of devicesfabricated on bulk polar, nonpolar and semipolar GaN substrates.Specifically for nonpolar and semipolar orientations, the lack of strongpolarisation induced electric fields that plague conventional devices onc-plane GaN leads to a greatly enhanced radiative recombinationefficiency in the light emitting InGaN layers. For polar materials, thedeleterious effects of polarization fields may be reduced by reducingthe InN content of the active region, and/or reducing the barrierthicknesses in multi-quantum well (MQW) active region structures. Also,for any surface orientation, the bulk native substrate provides forsimplified device geometry that may be scaled down to provide lowercosts (in dollars per lumen) compared to approaches based on foreignsubstrates like sapphire SiC, or Si. Furthermore, the reduceddislocation densities provided by bulk GaN offer assurance of highreliability at high current densities, which is not guaranteed byforeign substrate approaches.

Of particular importance to the field of lighting is the progress oflight emitting diodes (LED) fabricated on nonpolar and semipolar GaNsubstrates. Such devices making use of InGaN light emitting layers haveexhibited record output powers at extended operation wavelengths intothe violet region (390-430 nm), the blue region (430-490 nm), the greenregion (490-560 nm), and the yellow region (560-600 nm). For example, aviolet LED, with a peak emission wavelength of 402 nm, was recentlyfabricated on an m-plane (1-100) GaN substrate and demonstrated greaterthan 45% external quantum efficiency, despite having no light extractionenhancement features, and showed excellent performance at high currentdensities, with minimal roll-over [K.-C. Kim, M. C. Schmidt, H. Sato, F.Wu, N. Fellows, M. Saito, K. Fujito, J. S. Speck, S. Nakamura, and S. P.DenBaars, “Improved electroluminescence on nonpolar m-plane InGaN/GaNquantum well LEDs”, Phys. Stat. Sol. (RRL) 1, No. 3, 125 (2007).].Similarly, a blue LED, with a peak emission wavelength of 468 nm,exhibited excellent efficiency at high power densities and significantlyless roll-over than is typically observed with c-plane LEDs [K. Iso, H.Yamada, H. Hirasawa, N. Fellows, M. Saito, K. Fujito, S. P. DenBaars, J.S. Speck, and S. Nakamura, “High brightness blue InGaN/GaN lightemitting diode on nonpoiar m-plane bulk GaN substrate”, Japanese Journalof Applied Physics 46, L960 (2007).]. Two promising semipolarorientations are the (10-1-1) and (11-22) planes. These planes areinclined by 62.0 degrees and by 58.4 degrees, respectively, with respectto the e-plane. University of California, Santa Barbara (UCSB) hasproduced highly efficient LEDs on (10-1-1) GaN with over 65 mW outputpower at 100 mA for blue-emitting devices [H. Zhong, A. Tyagi, N.Fellows, F. Wu, R. B. Chung, M. Saito, K. Fujito, J. S. Speck, S. P.DenBaars, and S. Nakamura, “High power and high efficiency blue lightemitting diode on freestanding semipolar (1011) bulk GaN substrate”,Applied Physics Letters 90, 233504 (2007)] and on (11-22) GaN with over35 mW output power at 100 mA for blue-green emitting devices [H. Zhong,A. Tyagi, N. N. Fellows, R. B. Chung, M. Saito, K. Fujito, J. S. Speck,S. P. DenBaars, and S. Nakamura, Electronics Lett. 43, 825 (2007)], over15 mW of power at 100 mA for green-emitting devices [H. Sato, A. Tyagi,H. Zhong, N. Fellows, R. B Chung, M. Saito, K. Fujito, J. S. Speck, S.P. DenBaars, and S. Nakamura, “High power and high efficiency greenlight emitting diode on free-standing semipolar (1122) bulk GaNsubstrate”, Physical Status Solidi—Rapid Research Letters 1, 162 (2007)]and over 15 mW for yellow devices [H. Sato, R. B. Chung, H. Hirasawa, N.Fellows, H. Masui, F. Wu, M. Saito, K. Fujito, J. S. Speck, S. P.DenBaars, and S. Nakamura, “Optical properties of yellow light-emittingdiodes grown on semipolar (1122) bulk GaN substrates,” Applied PhysicsLetters 92, 221110 (2008).]. The UCSB group has shown that the indiumincorporation on semipolar (11-22) GaN is comparable to or greater thanthat of c-plane GaN, which provides further promise for achieving highcrystal quality extended wavelength emitting InGaN layers.

A non-polar or semi-polar LED may be fabricated on a bulk galliumnitride substrate. The gallium nitride substrate may be sliced from aboule that was grown by hydride vapor phase epitaxy or ammonothermally,according to methods known in the art. In one specific embodiment, thegallium nitride substrate is fabricated by a combination of hydridevapor phase epitaxy and ammonothermal growth, as disclosed in U.S.Patent Application No. 61/078,704, commonly assigned, and herebyincorporated by reference herein. The boule may be grown in thec-direction, the m-direction, the a-direction, or in a semi-polardirection on a single-crystal seed crystal. Semipolar planes may bedesignated by (hkil) Miller indices, where i=−(h+k), l is nonzero and atleast one of h and k are nonzero. The gallium nitride substrate may becut, lapped, polished, and chemical-mechanically polished. The galliumnitride substrate orientation may be within ±5 degrees, ±2 degrees, ±1degree, or ±0.5 degrees of the {1-100} m plane, the {11-20} a plane, the{11-22} plane, the {20-2±1} plane, the {1-10±1} plane, the {10-1±1}plane, the {1-10−±2} plane, or the {1-10±3} plane. The gallium nitridesubstrate may have a dislocation density in the plane of the large-areasurface that is less than 10⁶ cm⁻², less than 10⁵ cm⁻², less than 10⁴cm⁻², or less than 10³ cm⁻². The gallium nitride substrate may have adislocation density in the c plane that is less than 10⁶ cm⁻², less than10⁵ cm⁻², less than 10⁴ cm⁻², or less than 10³ cm⁻².

A homoepitaxial non-polar or semi-polar LED is fabricated on the galliumnitride substrate according to methods that are known in the art, forexample, following the methods disclosed in U.S. Pat. No. 7,053,413,which is hereby incorporated by reference in its entirety. At least oneAl_(x)In_(y)Ga_(1-x-y)N layer, where 0≦x≦1, 0≦y≦1, and 0≦x+y≦1, isdeposited on the substrate, for example, following the methods disclosedby U.S. Pat. Nos. 7,338,328 and 7,220,324, which are hereby incorporatedby reference in their entirety. The at least one Al_(x)In_(y)Ga_(1-x-y)Nlayer may be deposited by metal-organic chemical vapor deposition, bymolecular beam epitaxy, by hydride vapor phase epitaxy, or by acombination thereof. In one embodiment, the Al_(x)In_(y)Ga_(1-x-y)Nlayer comprises an active layer that preferentially emits light when anelectrical current is passed through it. In one specific embodiment, theactive layer comprises a single quantum well, with a thickness betweenabout 0.5 nm and about 40 nm. In a specific embodiment, the active layercomprises a single quantum well with a thickness between about 1 nm andabout 5 nm. In other embodiments, the active layer comprises a singlequantum well with a thickness between about 5 nm and about 10 nm,between about 10 nm and about 15 nm, between about 15 nm and about 20nm, between about 20 nm and about 25 nm, between about 25 nm and about30 nm, between about 30 nm and about 35 nm, or between about 35 nm andabout 40 nm. In another set of embodiments, the active layer comprises amultiple quantum well. In still another embodiment, the active regioncomprises a double heterostructure, with a thickness between about 40 nmand about 500 nm. In one specific embodiment, the active layer comprisesan In_(y)Ga_(1-y)N layer, where 0≦y≦1. Of course, there can be othervariations, modifications, and alternatives.

Furthermore, as the input current in a light emitting diode isincreased, the optical output power increases as the associated highernumber of injected electrons are converted into photons. In an “ideal”LED the light output would continue increasing linearly with increasedcurrent such that small LEDs could be driven to very high currentdensities to achieve high output power. In practice, however, this lightoutput versus current input characteristic of light emitting diodes hasbeen fundamentally limited by a phenomenon where the radiativeefficiency of conventional light emitting diodes decreases as thecurrent density increases. It has been observed that such phenomenacauses rollover or a sublinear increase in output power versus current.This results in only marginal increase in total flux as the inputcurrent is increased.

FIG. 3 shows a sample plot of relative luminous flux as a function ofinjection current for a conventional LED, a Cree XP-E white LED withjunction temperature of 25° C. The plot shows that the relative luminousflux at 350 mA (approximately 30-50 A/cm²) is 100% while at 700 mA therelative luminous flux is only approximately 170%. This shows that for aconventional LED a roll-off in efficiency for the LED of approximately15% occurs over the operating range from approximately 30-50 A/cm² to60-100 A/cm². In addition, the peak efficiency for this diode occurs atan even lower operating current density, indicating that the roll-off inefficiency from the peak value is even greater than 15% were the diodeto fee operated at 700 mA.

Due to the phenomenon, conventional light emitting diodes are typicallyoperated at lower current densities than provided by the present methodand devices, ranging from 10 A/cm² to 100 A/cm². This operating currentdensity restriction has placed practical limits on the total flux thatis possible from a single conventional light emitting diode. Commonapproaches to increase the flux, from an LED package include increasingthe active area of the LED (thereby allowing the LED to have a higheroperating current while maintaining a suitably low current density), andpackaging several LED die into an array of LEDs, whereby the totalcurrent is divided amongst the LEDs in the package. While theseapproaches have the effect of generating more total flux per LED packagewhile maintaining a suitably low current density, they are inherentlymore costly due to the requirement of increased total LED die area. Inone or more embodiments, we propose a method and device for lightingbased on one or more small-chip high brightness LEDs offering highefficiency operating at current densities in excess of conventionalLEDs, while maintaining a long operating lifetime.

There is a large body of work that establishes conventional knowledge ofthe limitations of operating LEDs at high current density with efficientoperation. This body of work includes the similarity in operatingcurrent density for high brightness LEDs that have been commercializedby the largest LED manufacturers, and a large body of work referencingthe “LED Droop” phenomena. Examples of commercial LEDs include Cree'sXP-E, XR-E, and MC-E packages and Lumileds K2 and Rebel packages, withone such example shown in FIG. 1. Similar high brightness LEDs areavailable from companies such as Osram, Nichia, Avago, Bridgelux, etc.that all operate in a current density range much lower than proposed inthis invention either through limiting the total current, increasing thedie size beyond 1 mm², or packaging multiple LED chips to effectivelyincrease the LED junction area. Examples of literature referencing andshowing the LED “droop” phenomena are described by Shen et al. inApplied Physics Letters, 91, 141101 (2007), and Michiue et. al. in theProceedings of the SPIE Vol. 7216, 72161Z-1 (2009) by way of example. Inaddition, Gardner et. al. l in Applied Physics Letters, 91, 243506(2007) explicitly state in reference to this phenomena and attempts toovercome it that typical current densities of interest for LEDs are20-400 A/cm² with their double heterostructure LED grown on a sapphiresubstrate showing a peak efficiency at approximately 200 A/cm² and thenrolling off above that operating point. In addition to the limits inmaintaining device efficiency while operating at high current density,it has been shown that as the current density is increased in lightemitting devices, the lifetime of the devices degrade below acceptablelevels with this degradation being correlated with dislocations in thematerial. Tomiya et. al. demonstrated in IEEE J. of Quantum Elec., Vol.10, No. 6 (2004) that light emitting devices fabricated on reduceddislocation density material allowed for higher current operationwithout the decrease in lifetime that was observed for devicesfabricated on high dislocation material. In their studies, dislocationreduction was achieved by means of lateral epitaxial overgrowth onmaterial grown heteroepitaxially. To date, conventional methods relatedto light emitting diodes related to alleviating or minimising the droopphenomena have not addressed growth and device design of light emittingdiodes grown and fabricated on bulk substrates. A further explanation ofconventional LED devices and their quantum efficiencies are described inmore detail below.

FIG. 4 is taken from N. F. Gardner et al., “Blue-emitting InGaN—GaNdouble-heterostructure light-emitting diodes reaching maximum quantumefficiency above 200 A/cm²”, Applied Physics Letters 91, 243500 (2007),show two types of variations in the external quantum efficiency as afunction of current density that are known in the prior art. Thebehavior shown in reference letters (a) and 2(b) of FIG. 4 arerepresentative of that of conventional LEDs. With one or more relativelythin quantum wells, for example, less than about 4 nanometers thick, theexternal quantum efficiency peaks at a current density of about 10amperes per square centimeter or less and drops relatively sharply athigher current densities. The external quantum efficiency at highercurrent densities can be increased by increasing the thickness of theactive layer, for example, to approximately 13 nanometers, as shown inFIG. 2( c). However, in this case the external quantum efficiency isvery low at current densities below about 30 amperes per squarecentimeter (A/cm²) and also at current densities above about 300 A/cm²,with a relatively sharp maximum in between. Ideal would be an LED withan external quantum efficiency that was approximately constant fromcurrent densities of about 20 A/mo^(t) to current densities above about200 A/cm², above about 300 A/cm², above about 400 A/cm², above about 500A/cm², or above about 1000 A/cm².

M. Schmidt et. al. in Jap. J. of Appl. Phys. Vol. 46, No. 7, 2007previously demonstrated an LED with a peak emission wavelength of 408 nmthat was grown on a bulk non-polar m-Plane substrate with a threadingdislocation density of less than 1×10⁶ cm². Despite the use of ahigh-quality bulk substrate with a non-polar orientation, the devicesdemonstrated in this work showed a roil-off in peak external quantumefficiency of approximately 5% over the relatively narrow operatingcurrent density of 11 to 111 A/cm², much lower than the values achievedin the current invention. These and other limitations of conventionaltechniques have been overcome in part by the present method and devices,which are described throughout the present specification and moreparticularly below.

FIG. 4A illustrates quantum efficiency plotted against current densityfor LED devices according to an embodiment of the present Invention. Asshown, the present devices are substantially free from current droop andis within a tolerance of about 10 percent, which is significant. Furtherdetails of the present device can be found throughout the presentspecification and more particularly below.

FIG. 5 is a simplified diagram of a high current density epitaxiallygrown LED structure according to an embodiment of the present invention.This diagram is merely an example, which should not unduly limit thescope of the claims herein. One of ordinary skill in the art wouldrecognize other variations, modifications, and alternatives. In one ormore embodiments, the LED structure includes at least:

-   1. A bulk GaN substrate, including a polar, semipolar or non-polar    surface orientation. Further comprising details provided below.    -   Any orientation, e.g., polar, non-polar, semi-polar, c-plane.    -   (Al,Ga,In)N based material    -   Threading dislocation (TD) density <10⁸ cm⁻²    -   Stacking fault (SF) density <10⁴ cm⁻¹    -   Doping >10¹⁷ cm⁻³-   2. An n-Type (Al)(In)GaN epitaxial layer(s) having a thickness    ranging from about 1 nm to about 10 μm and a dopant concentration    ranging from about 1×10¹⁶ cm⁻³ to about 5×10²⁰ cm⁻³. A Further    comprising details provided below.    -   Thickness <2 nm, <1 um, <0.5 um, <0.2 um    -   (Al,Ga,In)N based material    -   Growth T<1200 C, <1000 C    -   Un-intentionally doped (UID) or doped-   3. A plurality of doped and/or undoped (Al)(In)GaN active region    layers. Further comprising details provided below.    -   At least one (Al,Ga,In)N based layer    -   Quantum Well (QW) structure with one ore more wells    -   QWs are >20 A, >50 A, >80 A in thickness    -   QW and n- and p-layer growth temperature identical, or similar    -   Emission wavelength <575 nm, <500 nm, <450 nm, <410 nm-   4. A p-Type (Al)(In)GaN epitaxial layer(s) having a thickness    ranging front about 10 nm to about 500 nm and a dopant concentration    ranging from about 1×10¹⁶ cm⁻³ to about 1×10²¹ cm⁻³. Further    comprising details provided below.    -   At least one Mg doped layer    -   Thickness <0.3 um, <0.1 um.    -   (Al,Ga,In)N based    -   Growth T<1100 C, <1000 C, <900 C    -   At least one layer acts as an electron blocking layer    -   At least one layer acts as a contact layer

In a specific embodiment and referring to FIG. 5, the bulk GaN substrateis sliced from a gallium nitride boule, lapped, polished, and chemicallymechanically polished according to methods that are known in the art. Insome embodiments, the gallium nitride boule is grown epitaxially on aseed crystal. In some embodiments, the gallium nitride boule is grownammonothermally. In other embodiments, the gallium nitride boule isgrown by hydride vapor phase epitaxy (HVPE). Alternatively, combinationsof these techniques can also exist. Polycrystalline gallium nitridesource material may be formed by heating a crucible containing at leastgallium in an atmosphere comprising at least one of ammonia, a hydrogenhalide, and an inert gas such as argon. The crucible may further containa getter material at a level of at least about 100 parts per million(ppm) with respect to the gallium. The getter may be selected from atleast alkaline earth metals, hafnium, titanium, vanadium, chromium,yttrium, zirconium, niobium, rare earth metals, hafnium, tantalum, andtungsten. The crucible may be placed within a reactor, heated to atemperature of at least about 400 degrees Celsius in an atmospherecomprising ammonia and a hydrogen halide for a period between about 30minutes and about 72 hours, and cooled according to one or moreembodiments. Further details of the process for synthesizing thepolycrystalline indium gallium nitride are described in U.S. PatentApplication Ser. No. 61/122,332, which is hereby incorporated byreference in its entirety. The resulting polycrystalline gallium nitridemay have an oxygen content provided as a group III metal oxide or as asubstitutional impurity within the gallium nitride that is less thanabout 10 parts per million (ppm), less than about 1 ppm, or less thanabout 0.1 ppm. Of course, there can be other variations, modifications,and alternatives.

At least one seed crystal may be provided for ammonothermal crystalgrowth according to a specific embodiment. In some embodiments the seedcrystal is a gallium nitride single crystal. The seed crystal may have awurtzite crystal structure. The seed crystal may have a dislocationdensity less than about 10⁸ cm⁻², less than about 10⁷ cm⁻², less thanabout 10⁶ cm⁻², less than about 10⁵ cm⁻², less than about 10⁴ cm⁻², orless than about less than about 10³ cm⁻². The large area faces of theseed crystal may comprise c-plane (0001) and/or (000-1), m-plane(10-10), a-plane (11-20), or a semi-polar orientation such as {10-1-1}or {11-22} or, more generally, (hkil), as specified by theBravais-Miller notation, where at least one of h and k is nonzero and 1is also nonzero. The seed crystal may comprise a non-gallium nitridematerial such as sapphire, silicon carbide, spinel, or the like. Theseed crystal may comprise at least one film of gallium nitride. The atleast one gallium nitride film may be grown by metallorganic chemicalvapor deposition (MOCVD), molecular beam epitaxy (MBE), hydride vaporphase epitaxy (HVPE), or liquid phase epitaxy (LPE). In someembodiments, both the front surface and the back surface of aheteroepitaxial seed material are coated by a film of gallium nitride,as described in U.S. Patent application Ser. No. 61/096,304, which ishereby incorporated by reference in its entirety. In a preferredembodiment, the lattice constants of the large-area surfaces of the seedcrystal are within 1%, 0.3%, 0.1%, 0.03%, 0.01%, 0.003%, or 0.001% ofthe lattice constants of the bulk gallium nitride crystal to be grown onthe seed crystal. At least two seed crystals may be mounted on a seed,rack, as described in U.S. Patent application Ser. No. 61/087,135, whichis hereby incorporated by reference in its entirety.

The polycrystalline gallium nitride and at least one seed crystal may beprovided to an autoclave or a capsule for placement within an internallyheated high pressure apparatus. Examples of suitable high pressureapparatus are described in U.S. patent application Ser. Nos. 12/133,304,12/133,365, 61/073,687, and 61/087,122, which are hereby incorporated byreference in their entirety. A mineralizer is also provided to theautoclave or capsule. The mineralizer may comprise a base, such as atleast one of an alkali metal, an alkali amide, an alkali imide, analkali amido-imide, an alkali azide, an alkali nitride, an alkalineearth metal, an alkaline earth amide, an alkaline earth azide, or analkaline earth nitride. The mineralizer may comprise an acid, such as atleast one of an ammonium halide, a hydrogen halide, gallium halide, or acompound that may be formed by reaction of two or more of gallium metal,indium metal, ammonia, and a hydrogen halide. In some embodiments themineralizer comprises two or more metal constituents, two or morehalogen constituents, and/or two or more compounds. Ammonia may also beprovided, at a percent fill between about 50% and about 98%, or betweenabout 60% and about 90%, and the capsule or autoclave sealed. Thecapsule or autoclave may be heated to a temperature of at least about400 degrees Celsius and a pressure of at least about 100 megapascal(MPa) in order to cause crystal growth upon at least one seed crystal.Additional details of the crystal growth process may be found in U.S.Patent Application Publication No. 2008/0087910.

The ammonothermally-grown crystalline group III metal nitride may becharacterized by a wurzite structure substantially free from any cubicentitles and have an optical absorption coefficient of about 3 cm⁻¹ andless at wavelengths between about 385 nanometers and about 750nanometers. An ammonothermally-grown gallium nitride crystal maycomprise a crystalline substrate member having a length greater thanabout 5 millimeters, have a wurtzite structure and be substantially freeof other crystal structures, the other structures being less than about0.1% in volume in reference to the substantially wurtzite structure, animpurity concentration greater than 10¹⁴ cm⁻¹, greater than 10¹⁵ cm⁻¹,or greater than 10¹⁶ cm⁻¹ of at least one of Li, Na, K, Rb, Cs, Mg, Ca,F, and Cl, and an optical absorption coefficient of about 2 cm⁻¹ andless at wavelengths between about 385 nanometers and about 750nanometers. The gallium nitride crystal may have an optical absorptioncoefficient of about 0.5 cm⁻¹ and less at wavelengths between about 385nanometers and about 750 nanometers. The ammonothermally-grown galliumnitride crystal may be an n-type semiconductor, with a carrierconcentration n between about 10¹⁶ cm⁻³ and 10²⁰ cm⁻³ and a carriermobility η, in units of centimeters squared per volt-second, such thatthe logarithm to the base 10 of η is greater than about=−0.01855n³+1.0671n²−20.599n+135.49. The ammonothermally-grown galliumnitride crystal may have a resistivity less than about 0.050 Ω-cm, lessthan about 0.025 Ω-cm, or less than about 0.010 Ω-cm. Theammonothermally-grown gallium nitride crystal may be a p-typesemiconductor, with a carrier concentration n between about 10¹⁶ and10⁻³ and 10²⁰ cm⁻³ and a carrier mobility η, in units of centimeterssquared per volt-second, such that the logarithm to the base 10 of η isgreater than about −0.6546n+12.809.

In another specific embodiment the bulk GaN substrate is prepared from aboule that was grown by a flux method. Examples of suitable flux methodsare described in U.S. Pat. No. 7,063,741 and in U.S. Patent ApplicationPublication 2006/0037529, each of which are hereby incorporated byreference in their entirety. A polycrystalline group III metal nitrideand at least one flux are placed in a crucible and inserted into afurnace. The furnace is heated and the polycrystalline group III metalnitride is processed in a molten flux at a temperature greater thanabout 400 degrees Celsius and a pressure greater than about oneatmosphere, during which at least a portion of the polycrystalline groupIII metal nitride is etched away and re-crystallized onto at least onegroup III nitride crystal. In yet another specific embodiment the bulkGaN substrate is prepared from a boule that was grown by hyride vaporphase epitaxy (HVPE). Of course, there can be other variations,modifications, and alternatives. Further details of the next stepsincluding growth sequences are explained throughout the presentspecification and more particularly below.

In a specific embodiment, the growth sequence includes at least (1)n-type epitaxial material; (2) active region; (3) electron blockingregion; and (4) p-type epitaxial material. Of course, there can be othervariations, modifications, and alternatives. Again, further details ofthe present method can be found throughout the present specification andmore particularly below.

In a specific embodiment, epitaxial layers are deposited on thesubstrate by metalorganic chemical vapor deposition (MOCVD) atatmospheric pressure. The ratio of the flow rate of the group Vprecursor (ammonia) to that of the group III precursor (trimethylgallium, trimethyl indium, trimethyl aluminum) during growth is betweenabout 3000 and about 12000. In a specific embodiment, a contact layer ofn-type (silicon-doped) GaN is deposited on the substrate, with athickness of less than 5 microns and a doping level of about 2×10¹⁸cm⁻³.

In a specific embodiment, an undoped InGaN/GaN multiple quantum well(MQW) is deposited as the active layer. The MQW active region has two totwenty periods, comprising alternating layers of 2-12 nm of InGaN and1-20 nm of GaN as the barrier layers. Next, a 5-30 nm undoped AlGaNelectron blocking layer is deposited on top of the active region. Inother embodiments, the multiple quantum wells can be configured slightlydifferently. Of course, there can be other variations, modifications,and alternatives. The substrate and resulting epitaxial surfaceorientation may be polar, nonpolar or semipolar. In one or more otherembodiments, the bulk wafer can be in an off-axis configuration, whichcauses formation of one or more smooth films. In or more preferredembodiments, the overlying epitaxial film and structures arecharacterized by a morphology being smooth and relatively free-frompyramidal hillocks. Further details of the off-axis configuration andsurface morphology can be found throughout the present specification andmore particularly below. As an example, however, details of the off cutembodiment is described in “Method and Surface Morphology of Non-PolarGallium Nitride Containing Substrates,” James Raring et al., U.S. Ser.No. 12/497,289 filed Jul. 2, 2009, which is hereby incorporated byreference in its entirety.

A method according to embodiments for forming a smooth epitaxial filmusing an offcut or miscut or off-axis substrate is outlined below.

-   -   1. Provide GaN substrate or boule;    -   2. Perform off-axis miscut of GaN substrate to expose desired        surface region or process substrate or boule (e.g., mechanical        process) to expose off axis oriented surface region;    -   3. Transfer GaN substrate into MOCVD process chamber;    -   4. Provide a carrier gas selected from nitrogen gas, hydrogen        gas, or a mixture of them;    -   5. Provide a nitrogen bearing species such as ammonia or the        like;    -   4. Raise MOCVD process chamber to growth temperature, e.g., 700        to 1200 Degrees Celsius;    -   5. Maintain the growth temperature within a predetermined range;    -   6. Combine the carrier gas and nitrogen hearing species such as        ammonia with group III precursors such as the indium precursor        species tri-methyl-indium and/or tri-ethyl-indium, the gallium        precursor species tri-methyl-gallium and/or tri-ethyl-gallium,        and/or the aluminum precursor tri-methyl aluminum into the        chamber;    -   7. Form an epitaxial film containing one or more of the        following layers GaN, InGaN, AlGaN, InAlGaN;    -   8. Cause formation of a surface region of the epitaxial gallium        nitride film substantially free from hillocks and other surface        roughness structures and/or features;    -   9. Repeat steps (7) and (8) for other epitaxial films to form        one or more device structures; and    -   10. Perform other desired processing steps.

In one specific embodiment for nonpolar orientation (10-10), the miscutsubstrate in step 2 has a surface orientation that is tilted by about0.1 degree from (10-10) toward (0001). In another specific embodiment,the miscut substrate in step 2 has a surface orientation that is tiltedby between about 0.1 degree and about 0.5 degree from (10-10) toward(0001). In still another specific embodiment, the miscut substrate instep 2 has a surface orientation that is tilted by between about 0.2degree and about 1 degree from (10-10) toward (0001). In yet anotherspecific embodiment, the miscut substrate in step 2 has a surfaceorientation that is tilted by between about 1 degree and about 3 degreesfrom (10-10) toward (0001).

In another specific embodiment, the miscut substrate in step 2 has asurface orientation that is tilted by about 0.1 degree from (10-10)toward (1-210). In another specific embodiment, the miscut substrate instep 2 has a surface orientation that is tilted by between about 0.1degree and about 0.5 degree from (10-10) toward (1-210). In stillanother specific embodiment, the miscut substrate in step 2 has asurface orientation that is tilted by between about 0.2 degree and about1 degree from (10-10) toward (1-210). In yet another specificembodiment, the miscut substrate in step 2 has a surface orientationthat is tilted by between about 1 degree and about 3 degrees from(10-10) toward (1-210).

The above sequence of steps provides a method according to an embodimentof the present invention. In a specific embodiment, the presentinvention provides a method and resulting crystalline epitaxial materialwith a surface region that is substantially smooth and free fromhillocks and the like for improved device performance. Although theabove has been described in terms of an off-axis surface configuration,there can be other embodiments having an on-axis configuration using oneor more selected process recipes, which have been described in moredetail throughout the present specification and more particularly below.Other alternatives can also be provided where steps are added, one ormore steps are removed, or one or more steps are provided in a differentsequence without departing from the scope of the claims herein.

As merely an example, the present method can use the following sequenceof steps in forming one or more of the epitaxial growth regions using anMOCVD tool operable at atmospheric pressure, or low pressure, in someembodiments.

-   -   1. Start;    -   2. Provide a crystalline substrate member comprising a backside        region and a surface region, which has been offcut or miscut or        off-axis;    -   3. Load substrate member into an MOCVD chamber;    -   4. Place substrate member on susceptor, which is provided in the        chamber, to expose the offcut or miscut or off axis surface        region of the substrate member;    -   5. Subject the surface region to a first flow (e.g., derived        from one or more precursor gases including at least an ammonia        containing species, a Group III species, and a first carrier        gas) in a first direction substantially parallel to the surface        region;    -   6. Form a first boundary layer within a vicinity of the surface        region;    -   7. Provide a second flow (e.g., derived from at least a second        carrier gas) in a second direction configured to cause change in        the first boundary layer to a second boundary layer;    -   8. Increase a growth rate of crystalline material formed        overlying the surface region of the crystalline substrate        member;    -   9. Continue crystalline material growth to be substantially free        from hillocks and/or other imperfections;    -   10. Cease flow of precursor gases to stop crystalline growth;    -   11. Perform other steps and repetition of the above, as desired;    -   12. Stop.

The above sequence of steps provides methods according to an embodimentof the present invention. As shown, the method uses a combination ofsteps including a way of forming a film of crystalline material usingMOCVD. In preferred embodiments, the present invention includesatmospheric pressure (e.g. 700-800 Torr) growth for formation of highquality gallium nitride containing crystalline films that are smooth andsubstantially free from hillocks, pyramidal hillocks, and otherimperfections that lead to degradation of the electrical or opticalperformance of the device, including droop. In some embodiments, amultiflow technique is provided.

FIG. 5A is one example of a simplified flow diagram for a method forfabricating an improved GaN film according to an embodiment of thepresent invention. The invention provides (step 503) a crystallinesubstrate member having a backside region and a surface region. Thecrystalline substrate member can include a gallium nitride wafer, or thelike. In a preferred embodiment, the substrate is bulk nonpolar (10-10)GaN substrate.

In a specific embodiment, the present method uses a miscut or offcutcrystalline substrate member or boule of GaN, but can be other materialsand does not imply use of a process of achieving the miscut or offcut.As used herein, the term “miscut” should be interpreted according toordinary meaning as understood by one of ordinary skill in the art. Theterm miscut is not intended to imply any undesirable cut relative to,for example, any of the crystal planes, e.g., c-plane, a-plane. The termmiscut is intended to describe a surface orientation slightly tiltedwith respect to, or vicinal to, a low-Miller-index surface crystal planesuch as the nonpolar (10-10) GaN plane. In other embodiments, the miscutsurface orientation is vicinal to a semipolar orientation such as the(10-1-1) family of planes, the (11-22) family of planes, the {20-21}family of planes or the {30-31} family of planes, but there can beothers. Additionally, the term “offcut” is intended to have a similarmeaning as miscut, although there could be other variations,modifications, and alternatives. In yet other embodiments, thecrystalline surface plane is not miscut and/or offcut but can beconfigured using a mechanical and/or chemical and/or physical process toexpose any one of the crystalline surfaces described explicitly and/orimplicitly herein. In specific embodiments, the term miscut and/oroffcut and/or off axis is characterized by at least one or moredirections and corresponding magnitudes, although there can be othervariations, modifications, and alternatives.

As shown, the method includes placing or loading (step 505) thesubstrate member into an MOCVD chamber. In a specific embodiment, themethod supplies one or more carrier gases, step 507, and one or morenitrogen bearing precursor gases, step 509, which are described in moredetail below. In one or more embodiments, the crystalline substratemember is provided on a susceptor from the backside to expose thesurface region of the substrate member. The susceptor is preferablyheated using resistive elements or other suitable techniques. In aspecific embodiment, the susceptor is heated (step 511) to a growthtemperature ranging from about 700 to about 1200 Degrees Celsius, butcan be others.

In a specific embodiment, the present method includes subjecting thesurface region of the crystalline substrate to a first flow in a firstdirection substantially parallel to the surface region. In a specificembodiment, the method forms a first boundary layer within a vicinity ofthe surface region. In a specific embodiment, the first boundary layeris believed to have a thickness ranging from about 1 millimeters toabout 1 centimeters, but can be others. Further details of the presentmethod can be found below.

Depending upon the embodiment, a flow is preferably derived from one ormore precursor gases including at least an ammonia containing species, aGroup III species (step 513), and a first carrier gas, and possiblyother entities. Ammonia is a Group V precursor according to a specificembodiment. Other Group V precursors include N₂. In a specificembodiment, the first carrier gas can include hydrogen gas, nitrogengas, argon gas, or other inert species, including combinations. In aspecific embodiment, the Group III precursors include TMGa, TEGa, TMIn,TMA1, dopants (e.g., Cp2Mg, disilane, silane, diethelyl zinc, iron,manganese, or cobalt containing precursors), and other species. Asmerely an example, a preferred combination of miscut/offcut/substratesurface configurations, precursors, and carrier gases are providedbelow.

-   -   Non-polar (10-10) GaN substrate surface configured −0.6 degrees        and greater or preferably −0.8 degrees and greater (and less        than −1.2 degrees) in magnitude toward c-plane (0001);    -   Carrier Gas: Any mixture of N₂ and H₂, but preferably all H₂;    -   Group V Precursor; NH₃; Group III Precursor: TMGa and/or TEGa        and/or TMIn and/or TEIn and/or TMA1; and    -   Optional Dopant Precursor: Disilane, silane, Cp₂Mg;        Or    -   Non-polar GaN substrate with no offcut or miscut;    -   Carrier Gas: all N₂; Group V Precursor: NH₃; Group III        Precursor: TMGa and/or TEGa and/or TMIn and/or TEIn and/or TMA1;        and    -   Optional Dopant Precursor: Disilane, silane, Cp₂Mg.

Depending upon the embodiment, the method also continues (step 515) withepitaxial crystalline material growth, which is substantially smooth andfree of hillocks or other imperfections. In a specific embodiment, themethod also can cease flow of precursor gases to stop growth and/orperform other steps. In a specific embodiment, the method stops at step517. In a preferred embodiment, the present method causes formation of agallium nitride containing crystalline material that has a surfaceregion that is substantially free of hillocks and other defects, whichlead to poorer crystal quality and can be detrimental to deviceperformance. In a specific embodiment, at least 90% of the surface areaof the crystalline material is free from pyramidal hillock structures.

The above sequence of steps provides methods according to an embodimentof the present invention. As shown, the method uses a combination ofsteps including a way of forming a film of crystalline material usingMOCVD. In preferred embodiments, the present invention includes a flowtechnique provided at atmospheric pressure for formation of high qualitygallium nitride containing crystalline films, which have surface regionssubstantially smooth and free from hillocks and other defects orimperfections. The above sequence of steps provides a method accordingto an embodiment of the present invention. In a specific embodiment, theresulting crystalline material is substantially free from hillocks forimproved device performance.

In one or more embodiments, a p-type GaN contact layer is deposited,with a thickness of about 200 nm and a hole concentration greater thanabout 5×10¹⁷ cm⁻³. An Ohmic contact layer is deposited onto the p-typecontact layer as the p-type contact and may be annealed to providedesired characteristics. Ohmic contact layers include Ag-based single ormulti-layer contacts, indium-tin-oxide (ITO) based contacts, Pd basedcontacts, Au based contacts, and others. LED mesas, with a size of about250×250 μm², are formed by photolithography and dry etching using achlorine-based inductively-coupled plasma (ICP) technique. As anexample, Ti/Al/Ni/Au is e-beam evaporated onto the exposed n-GaN layerto form the n-type contact. Ti/Au may be e-beam evaporated onto aportion of the p-type contact layer to form a p-contact pad, and thewafer is diced into discrete LED dies using techniques such as laserscribe and break, diamond scribe and break, sawing, water-jet cutting,laser ablation, or others. Electrical connections are formed byconventional die-attach and wire bonding steps.

FIG. 6 is a simplified diagram illustrating a high current density LEDstructure with electrical connections according to an embodiment of thepresent invention. This diagram is merely an illustration, which shouldnot unduly limit the scope of the claims herein. One of ordinary skillin the art would recognize other variations, modifications, andalternatives. As shown, the LED structure is characterized as atop-emitting lateral conducting high current density LED according to aspecific embodiment. Preferably, the LED structure includes at least:

-   1. A bulk GaN substrate, including polar, semipolar or non-polar    surface orientation;-   2. An n-Type (Al)(In)GaN epitaxial layer(s) having a thickness    ranging from about 1 nm to about 10 μm and a dopant concentration    ranging from about 1×10¹⁶ cm⁻³ to about 5×10²⁰ cm⁻³;-   3. A plurality of doped and/or undoped (Al)(In)GaN Active Region    layers;-   4. A p-Type (Al)(In)GaN epitaxial layer(s) having a thickness    ranging from about 10 nm to about 500 nm and a dopant concentration    ranging from about 1×10¹⁶ cm⁻³ to about 1×10²¹ cm⁻³;-   5. A semi-transparent p-type contact made of a suitable material    such as indium tin oxide, zinc oxide and having a thickness ranging    from about 5 nm to about 500 nm; and-   6: An n-type contact made of a suitable material such as Ti/Al/Ni/Au    or combinations of these metals, Ti/Al/Ti/Au or combinations of    these metals having a thickness ranging from about 100 nm to about 7    μm.

FIG. 7 is a simplified diagram of a substrate-emitting lateralconducting (i.e., “flip-chip”) high current density LED device accordingto an embodiment of the present invention. In this embodiment, the LEDdevice includes at least:

-   1. A bulk GaN substrate;-   2. An n-Type (Al(In)GaN epitaxial layer(s);-   3. A plurality of doped and/or undoped (Al)(In)GaN Active Region    layers;-   4. A p-Type (Al)(In)GaN epitaxial layer(s);-   5. A reflective p-type contact; and-   6. An n-type contact.

FIG. 8 is a simplified diagram of a substrate-emitting verticallyconducting high current density LED according to a specific embodimentof the present invention. The LED device includes at least:

-   1. A bulk GaN substrate;-   2. An n-Type (Al)(In)GaN epitaxial layer(s);-   3. A plurality of doped and/or undoped (Al)(In)GaN Active Region    layers;-   4. A p-Type (Al)(In)GaN epitaxial layer(s);-   5. A reflective p-type contact; and-   6. An n-type contact.

FIG. 9 is a simplified example of a packaged white LED containing a highcurrent density LED device according to an embodiment of the presentinvention. In a specific embodiment, the packaged LED device includes atleast:

-   1. A high current density LED device;-   2. An encapsulant or lens material which may or may not contain a    combination of red, green, blue, orange, yellow emitting or other    color down-conversion materials in a configuration such that white    light is produced when the down-conversion materials are contained    in the encapsulant or lens; and-   3. An LED package that provides electrical connection to the LED and    a path for thermal dissipation from the subject invention to the    surrounding environment.

Other examples of packaged devices can be found in U.S. Ser. No.61/244,443 filed Sep. 21, 2009, entitled “Reflection Mode WavelengthConversion Material for Optical Devices Using Non-Polar or SemipolarGallium Containing Materials,” Trottier et al. (Attorney Docket No.027364-007200US), commonly owned, and hereby incorporated by reference.In other embodiments, the packaged device includes an arrayconfiguration such as described in “White Light Apparatus and Method” toShum, Ser. No. 61/301,193, filed Feb. 2, 2010, commonly assigned, andhereby incorporated by reference. The present LED device can beconfigured in an array formed on a substrate member.

FIG. 10 is a simplified diagram showing pulsed output power vs. currentdensity and external quantum efficiency vs. current density for an LEDfabricated on nonpolar GaN with an emission wavelength of ˜405 nmaccording to one or more embodiments. This diagram is merely anillustration, which should not unduly limit the scope of the claimsherein. One of ordinary skill in the art would recognize othervariations, modifications, and alternatives. Of particular mention isthe small decrease in external quantum efficiency up to approximatelyfour times higher operating current density than for conventional LEDsthat have been fabricated in the prior art. Other examples were providedin FIG. 4A.

In a preferred embodiment, the device uses an Indium Tin Oxide (ITO) asa contact material configured for operation at high current density. Ina preferred embodiment, the high current density is 200 amps/cm², forexample as high as 500 amps/c², or even 1000 amps/cm² and greater. TheITO material is substantially free from degradation, and tree fromimperfections.

The junction temperature of the LED under operating conditions isgreater than about 100 degrees Celsius, and often greater than about 150degrees Celsius, or even above about 200 degrees Celsius. In someembodiments, the LED is able to operate in continuous wave (CW) modewithout active cooling, and in some cases without passive cooling.

In other embodiments, the present invention provides a resulting deviceand method using bulk gallium and nitrogen containing material forimproved reliability. That is, growth on the bulk GaN substratesincreases reliability at the high current densities. In contrast,conventional LEDs grown on foreign substrates are imperfect and includemultiple defects. It is believed that such defects caused by thehetereoepitaxial growth limit the device lifetime and therefore prohibitoperation a high current densities. The LEDs according to one or moreembodiments should not suffer from the same defects. In a preferredembodiment, the lifetime windows are >500 hrs CW, >1000 hrs CW, >2000hrs CW, >5000 hrs CW, or others.

In a specific embodiment, the present invention also includes LED basedlighting fixtures and replacement lamps. As an example, goals of theselighting fixtures are to produce an acceptable level of light (totallumens), of a desirable appearance (color temperature and CRI), with ahigh efficacy (lm/W), at a low cost. While these characteristics are alldesirable, there are typically design trades that must be consideredwhich result in some, but not all of the requirements being met. In thepresent invention, we propose LED based fixtures and lamps that arebased on light emitting diodes grown on bulk III-Nitride substrates suchas a bulk gallium nitride substrate. These LEDs exhibit surprisinglydifferent performance characteristics compared with conventional LEDsthat are grown heteroepitaxially on foreign substrates such as sapphire,silicon carbide, silicon, zinc oxide, and the like. The characteristicsthat these bulk III-Nitride based LEDs exhibit enable very differentlamp/fixture designs that are currently not believed to be possible withconventional LEDs.

Conventional light sources, incandescent, halogen, fluorescent, HID, andthe like have well defined standard characteristics. Thisstandardization allows for a high degree of knowledge on the operatingcharacteristics that are required from LED based lamps when designinglight sources that are made to be replacements for the incumbenttechnology. While there is a vast array of lighting products on themarket, there are a large number of standard lamps or fixtures that havebeen the subject of intense research for LED based replacementsolutions. Some examples of these lamp/fixtures, while not exhaustive,include A-lamps, fluorescent tubes, compact CFL's, metallic reflectorsof various sizes (MR), parabolic reflectors of various sizes (PAR),reflector bulbs (R), single and double ended quartz halogens,candelabra's, globe bulbs, high bays, troffers, and cobra-heads. A givenlamp will have characteristic luminous outputs that are dictated by theinput power to the lamp. For example, a 20 W MR-16 fixture willtypically emit approximately 300 lm, a 30 W MR-16, 450 lm, and a 50 WMR-16 will emit 700 lm. To appropriately replace these fixtures with anLED solution, the lamp must conform to the geometrical sizing for MR16lamps, and reach minimum levels of luminous flux.

Despite these specified guidelines, there are relatively few truereplacement lamps that are designed with LEDs that reach the luminousflux desired and have either a comparable or higher luminous efficacy,motivating the end user to switch from the incumbent technology. Thoseproducts that do meet these requirements are prohibitively expensivewhich has led to extremely slow adoption. A large portion of this costis dictated by the number of LEDs required for LED based lamps to reachthe luminous flux and luminous efficacy of current technology. This hasoccurred despite the high luminous efficacy that is typically reportedfor LEDs, which is much lower in an SSL lamp than specified as adiscrete device.

FIG. 11 shows a typical LED de-rating that SSL users assume when usingLEDs in a SSL application. The LEDs typically have to be de-rated fromtheir specified performance to account for increased temperature duringoperation, optical loss, electrical conversion losses, and lumendepreciation over time. Reduced efficacy and total flux as a function oftemperature is extremely problematic because beating results both fromthe minimal heat sink volume in typical lamp fixtures, and additionalheating that occurs as the end user increases the input current in anattempt to increase the output flux.

As an example of the performance limitations of current LED based lamps,FIG. 12 shows cumulative data that was measured as part of the U.S.Department of Energy Caliper Testing program on MR16 light lamps. FIG.12 shows that to replicate the output power of a 20 W halogen bulb, theLED equivalent must generate at least 270 lumens of flux with a luminousefficacy in excess of 13 lm/W. While even with de-rating, the resultsshow that most products exceed the luminous efficacy of the halogenincumbent, only one product generated enough total flux to claimequivalence to a 20 W MR16. In addition, this product achieved this fluxby mounting a large number (>4) of high power LEDs into the MR16fixture, resulting in a fixture with greater than 4 mm² of LED junctionactive area. The cost of the lamp increases approximately linearly asthe total junction active area for the LEDs increases. Thus, it ishighly desirable to decrease the total active junction area of LED thatis contained within a given lamp, while still maintaining the desiredtotal flux and efficacy.

Typical LEDs that are grown heteroepitaxially are unable to maintainhigh flux while decreasing the active area size because of current andthermal “droop”. As the current density is increased in an LED, therelative efficiency has been shown to decrease. This effect can resultin a decrease in relative radiative efficiency from 100% at ˜10 A/cm² to50% at ˜100 A/cm².

LED radiative efficiency has also been shown to decrease as a functionof the temperature of the junction of the LED. As the LED junction areadecreases, the thermal resistance of the LED to package bond increasesbecause the area for thermal flow is decreased. In addition to this, thecurrent density increase that's associated with the decreasing arearesults in lower radiative efficiency as described above and thus morepower that is required to be dissipated as heat. Further details ofperformance characteristics of conventional LED devices as compared tothe present techniques are provided below. As shown, the presenttechniques and device lead to higher lumens per square area.

As used herein, the term GaN substrate is associated with GroupIII-nitride based materials including GaN, InGaN, AlGaN, or other GroupIII containing alloys or compositions that are used as startingmaterials. Such starting materials include polar GaN substrates (i.e.,substrate where the largest area surface is nominally an (h k l) planewherein h=k=0, and 1 is non-zero), non-polar GaN substrates (i.e.,substrate material where the largest area surface is oriented at anangle ranging from about 80-100 degrees from the polar orientationdescribed above towards an (h k l) plane wherein l=0, and at least oneof h and k is non-zero) or semi-polar GaN substrates (i.e., substratematerial where the largest area surface is oriented at an angle rangingLoot about +0.1 to 80 degrees or 110-179.9 degrees from the polarorientation described above towards an (h k l) plane wherein l=0, and atleast one of h and k is non-zero).

While the above is a full description of the specific embodiments,various modifications, alternative constructions and equivalents may beused. Although the specification describes one or more specific galliumand nitrogen containing surface orientations, it would be recognizedthat any one of a plurality of family of plane orientations can be used.Therefore, the scope of the present invention which is defined by theappended claims.

What is claimed is:
 1. A method of using a light emitting diode, themethod comprising: providing a fixture comprising the light emittingdiode, the light emitting diode comprising: a bulk gallium and nitrogencontaining substrate having a surface region; and at least one activeregion formed overlying the surface region; a current density from 175Amps/cm² to 2,000 Amps/cm² characterizing the at least one activeregion; and wherein the light emitting diode is characterized by anexternal quantum efficiency (EQE) of at least 50%, and a peak emissionwavelength between about 385 nm and about 480 nm; and emittingelectromagnetic radiation having the peak emission wavelength betweenabout 385 nm and 480 nm.
 2. The method of claim 1, wherein the bulkgallium and nitrogen containing substrate is characterized by a growthon a non-polar orientation.
 3. The method of claim 1, wherein the bulkgallium and nitrogen containing substrate is characterized by a growthorientation in on at least one of a plurality of semi-polar crystalplanes selected from the (10-1-1), (11-22), (20-21), (20-2-1), (30-31),(30-3-1), (30-32), and (30-3-2) crystal plane, and an offcut of any oneof these planes within +/−5 degrees toward the c-direction and/or thea-direction.
 4. The method of claim 1, further comprising at least onephosphor operably coupled to the at least one active region to produce awhite light emission.
 5. The method of claim 1, further comprising ajunction area from about 0.0002 mm² to about 1 mm².
 6. The method ofclaim 1, wherein the bulk gallium and nitrogen containing substratecomprises at least one region characterized by a surface dislocationdensity below about 10⁶ cm⁻².
 7. The method of claim 1, furthercomprising an n-type contact electrically coupled to a first side of theat least one active region and a p-type contact electrically coupled toa second side of the at least one active region to form a verticallyconducting characteristic.
 8. The method of claim 1, wherein the atleast one active region is characterized by a junction temperaturegreater than about 100 degrees Celsius.
 9. The method of claim 1,wherein the bulk gallium and nitrogen containing substrate ischaracterized by an optical absorption coefficient of less than about 3cm⁻¹ at wavelengths between about 385 nanometers and about 750nanometers.
 10. The method of claim 1, wherein the bulk gallium andnitrogen containing substrate is characterized by a resistivity lessthan about 0.050 ohm-cm.
 11. The method of claim 1, wherein the bulkgallium and nitrogen containing substrate is an n-type semiconductor,with a carrier concentration n between about 10¹⁶ cm⁻³ and 10²⁰ cm⁻³ anda carrier mobility η, in units of centimeters squared per volt-second,such that the logarithm to the base 10 of η is greater than about−0.018557n³+1.0671n²−20.599n+135.49.
 12. The method of claim 1, whereinthe at least one active region comprises a total active layer thicknessof at least 20 nm.
 13. The method of claim 1, wherein the currentdensity is from 400 Amps/cm² to 800 Amps/cm².
 14. The method of claim 1,wherein the current density is from 200 Amps/cm² to 1,000 Amps/cm². 15.The method of claim 1, wherein the current density is from 500 Amps/cm²to 1,000 Amps/cm².
 16. The method of claim 1, wherein the currentdensity is from 1,000 Amps/cm² to 2,000 Amps/cm².
 17. The method ofclaim 1, wherein the bulk gallium and nitrogen containing substrate ischaracterized by a growth on a polar orientation.
 18. The method ofclaim 1, wherein the bulk gallium and nitrogen containing substrate isgrown epitaxially, ammonothermally, by hydride vapor phase-epitaxy, bymetalorganic chemical vapor deposition, by molecular beam epitaxy, byliquid phase epitaxy, by a flux method, or by a combination of any ofthe foregoing.
 19. The method of claim 1, wherein the bulk gallium andnitrogen containing substrate comprises at least one regioncharacterized by a surface dislocation density below about 10⁷ cm⁻². 20.The method of claim 1, wherein the light emitting diode is operable in acontinuous wave mode.
 21. The method of claim 1, wherein the lightemitting diode is operable in a pulsed mode.
 22. The method of claim 1,wherein the light emitting diode is characterized by a lumens per activejunction area greater than 300 lm/mm², for a warm white emission with acorrelated color temperature (CCT) of less than about 5,000K, and acolor rendering index (CRI) greater than
 75. 23. The method of claim 1,wherein the bulk gallium and nitrogen containing substrate ischaracterized by a growth on a polar orientation.
 24. The method ofclaim 1, wherein the bulk gallium and nitrogen containing substrate ischaracterized by a growth on a c-plane orientation.
 25. A method ofusing a light emitting diode, the method comprising: providing a fixturecomprising the light emitting diode, the light emitting diodecomprising: a bulk gallium and nitrogen containing substrate comprisinga surface region characterized by a c-plane orientation; one or moren-type epitaxial layers overlying the surface region; at least oneactive region formed overlying the one or more n-type epitaxial layers,wherein the at least one active region comprises one or more activelayers, a current density from 175 Amps/cm² to 2,000 Amps/cm²characterizing the at least one active region; one or more p-typeepitaxial layers overlying the at least one active region; at least onereflective p-type contact overlying the one or more p-type epitaxiallayers and electrically coupled to a first side of the at least oneactive region; and at least one n-type contact electrically coupled to asecond side of the at least one active region; wherein the lightemitting diode is characterized by an external quantum efficiency (EQE)of at least 50%, and a peak emission wavelength between about 385 nm andabout 480 nm; and emitting electromagnetic radiation having the peakemission wavelength between about 385 nm and 480 nm.
 26. The method ofclaim 25, wherein the c-plane is selected from the (0001) plane, the(000-1) plane, and an offcut of any one of these planes.
 27. The methodof claim 25, further comprising at least one phosphor operably coupledto the at least one active region to produce a white light emission. 28.The method of claim 25, further comprising a junction area from about0.0002 mm² to about 1 mm².
 29. The method of claim 25, wherein the bulkgallium and nitrogen containing substrate comprises at least one regioncharacterized by a surface dislocation density below about 10⁶ cm⁻². 30.The method of claim 25, wherein the active region is characterized by ajunction temperature greater than about 100 degrees Celsius.
 31. Themethod of claim 25, wherein the bulk gallium and nitrogen containingsubstrate is characterized by an optical absorption coefficient of lessthan about 3 cm⁻¹ at wavelengths between about 385 nanometers and about750 nanometers.
 32. The method of claim 25, wherein the bulk gallium andnitrogen containing substrate is characterized by a resistivity lessthan about 0.050 ohm-cm.
 33. The method of claim 25, wherein the bulkgallium and nitrogen containing substrate is an n-type semiconductor,with a carrier concentration n between about 10¹⁶ cm⁻³ and 10²⁰ cm⁻³ anda carrier mobility η, in units of centimeters squared per volt-second,such that the logarithm to the base 10 of η is greater than about−0.018557n³+1.0671n²-20.599n+135.49.
 34. The method of claim 25, whereinthe at least one active region comprises a total active layer thicknessof at least 20 nm.
 35. The method of claim 25, wherein the currentdensity is from 400 Amps/cm² to 800 Amps/cm².
 36. The method of claim25, wherein the current density is from 200 Amps/cm² to 1,000 Amps/cm².37. The method of claim 25, wherein the current density is from 500Amps/cm² to 1,000 Amps/cm².
 38. The method of claim 25, wherein thecurrent density is from 1,000 Amps/cm² to 2,000 Amps/cm².
 39. The methodof claim 25, wherein the at least one n-type contact is adjacent the atleast one n-type epitaxial layer, is adjacent the substrate, or acombination thereof.
 40. The method of claim 25, wherein the bulkgallium and nitrogen containing substrate is grown epitaxially,ammonothermally, by hydride vapor phase-epitaxy, by metalorganicchemical vapor deposition, by molecular beam epitaxy, by liquid phaseepitaxy, by a flux method, or by a combination of any of the foregoing.41. The method of claim 25, wherein the bulk gallium and nitrogencontaining substrate comprises at least one region characterized by asurface dislocation density below about 10⁷ cm⁻².
 42. The method ofclaim 25, wherein the light emitting diode is operable in a continuouswave mode.
 43. The method of claim 25, wherein the light emitting diodeis operable in a pulsed mode.
 44. The method of claim 25, wherein thelight emitting diode is characterized by a lumens per active junctionarea of greater than 300 lm/mm², for a warm white emission with acorrelated color temperature (CCT) of less than about 5,000K, and acolor rendering index (CRI) greater than
 75. 45. A method of using alight emitting diode, the method comprising: providing a fixturecomprising a light emitting diode, the light emitting diode comprising:a bulk gallium and nitrogen containing substrate having a surface regioncharacterized by a semipolar orientation; and at least one active regionformed overlying the surface region, a current density from 175 Amps/cm²to 2,000 Amps/cm² characterizing the at least one active region; whereinthe light emitting diode is characterized by an external quantumefficiency (EQE) of at least 50%, and a peak emission wavelength betweenabout 385 nm and about 480 nm; and emitting electromagnetic radiationhaving the peak emission wavelength between about 385 nm and 480 nm. 46.The method of claim 45, wherein the semipolar orientation is selectedfrom the (10-1-1), (11-22), (20-21), (20-2-1), (30-31), (30-3-1),(30-32), and (30-3-2) crystal plane, and an offcut of any one of theseplanes within +/−5 degrees toward the c-direction and/or thea-direction.
 47. The method of claim 45, further comprising at least onephosphor operably coupled to the at least one active region to produce awhite light emission.
 48. The method of claim 45, further comprising ajunction area from about 0.0002 mm² to about 1 mm².
 49. The method ofclaim 45, wherein the bulk gallium and nitrogen containing substratecomprises at least one region characterized by a surface dislocationdensity below about 10⁶ cm⁻².
 50. The method of claim 45, furthercomprising an n-type contact electrically coupled to a first side of theat least one active region and a p-type contact electrically coupled toa second side of the at least one active region to form a verticallyconducting characteristic.
 51. The method of claim 45, wherein theactive region is characterized by a junction temperature greater thanabout 100 degrees Celsius.
 52. The method of claim 45, wherein the bulkgallium and nitrogen containing substrate is characterized by an opticalabsorption coefficient of less than about 3 cm⁻¹ at wavelengths betweenabout 385 nanometers and about 750 nanometers.
 53. The method of claim45, wherein the bulk gallium and nitrogen containing substrate ischaracterized by a resistivity less than about 0.050 ohm-cm.
 54. Themethod of claim 45, wherein the bulk gallium and nitrogen containingsubstrate is an n-type semiconductor, with a carrier concentration nbetween about 10¹⁶ cm⁻³ and 10²⁰ cm⁻³ and a carrier mobility η, in unitsof centimeters squared per volt-second, such that the logarithm to thebase 10 of η is greater than about −0.018557n³+1.0671n²-20.599n+135.49.55. The method of claim 45, wherein the at least one active regioncomprises a total active layer thickness of at least 20 nm.
 56. Themethod of claim 45, wherein the current density is from 400 Amps/cm² to800 Amps/cm².
 57. The method of claim 45, wherein the current density isfrom 200 Amps/cm² to 1,000 Amps/cm².
 58. The method of claim 45, whereinthe current density is from 500 Amps/cm² to 1,000 Amps/cm².
 59. Themethod of claim 45, wherein the current density is from 1,000 Amps/cm²to 2,000 Amps/cm².
 60. The method of claim 45, wherein the bulk galliumand nitrogen containing substrate is grown epitaxially, ammonothermally,by hydride vapor phase-epitaxy, by metalorganic chemical vapordeposition, by molecular beam epitaxy, by liquid phase epitaxy, by aflux method, or by a combination of any of the foregoing.
 61. The methodof claim 45, wherein the bulk gallium and nitrogen containing substratecomprises at least one region characterized by a surface dislocationdensity below about 10⁷ cm⁻².
 62. The method of claim 45, wherein thelight emitting diode is operable in a continuous wave mode.
 63. Themethod of claim 45, wherein the light emitting diode is operable in apulsed mode.
 64. The method of claim 45, wherein the light emittingdiode is characterized by a lumens per active junction area greater than300 lm/mm², for a warm white emission with a correlated colortemperature (CCT) of less than about 5,000K, and a color rendering index(CRI) greater than
 75. 65. A method of using a light emitting diode, themethod comprising: providing a fixture comprising a light emittingdiode, the light emitting diode comprising: a bulk gallium and nitrogencontaining substrate having a surface region characterized by a nonpolarorientation; and at least one active region formed overlying the surfaceregion, a current density from 175 Amps/cm² to 2,000 Amps/cm²characterizing the at least one active region; wherein the lightemitting diode is characterized by an external quantum efficiency (EQE)of at least 50%, and a peak emission wavelength between about 385 nm andabout 480 nm; and emitting electromagnetic radiation having the peakemission wavelength between about 385 nm and 480 nm.
 66. The method ofclaim 65, wherein the nonpolar orientation is selected from the (10-10)plane and a miscut from 0.1 degrees to 3 degrees toward the (0001) planeor the (1-210) plane.
 67. The method of claim 65, further comprising atleast one phosphor operably coupled to the at least one active region toproduce a white light emission.
 68. The method of claim 65, furthercomprising a junction area from about 0.0002 mm² to about 1 mm².
 69. Themethod of claim 65, wherein the bulk gallium and nitrogen containingsubstrate comprises at least one region characterized by a surfacedislocation density below about 10⁶ cm⁻².
 70. The method of claim 65,further comprising an n-type contact electrically coupled to a firstside of the at least one active region and a p-type contact electricallycoupled to a second side of the at least one active region to form avertically conducting characteristic.
 71. The method of claim 65,wherein the active region is characterized by a junction temperaturegreater than about 100 degrees Celsius.
 72. The method of claim 65,wherein the bulk gallium and nitrogen containing substrate ischaracterized by an optical absorption coefficient of less than about 3cm⁻¹ at wavelengths between about 385 nanometers and about 750nanometers.
 73. The method of claim 65, wherein the bulk gallium andnitrogen containing substrate is characterized by a resistivity lessthan about 0.050 ohm-cm.
 74. The method of claim 65, wherein the bulkgallium and nitrogen containing substrate is an n-type semiconductor,with a carrier concentration n between about 10¹⁶ cm⁻³ and 10²⁰ cm⁻³ anda carrier mobility η, in units of centimeters squared per volt-second,such that the logarithm to the base 10 of η is greater than about−0.018557n³+1.0671n²-20.599n+135.49.
 75. The method of claim 65, whereinthe at least one active region comprises a total active layer thicknessof at least 20 nm.
 76. The method of claim 65, wherein the currentdensity is from 400 Amps/cm² to 800 Amps/cm².
 77. The method of claim65, wherein the current density is from 200 Amps/cm² to 1,000 Amps/cm².78. The method of claim 65, wherein the current density is from 500Amps/cm² to 1,000 Amps/cm².
 79. The method of claim 65, wherein thecurrent density is from 1,000 Amps/cm² to 2,000 Amps/cm².
 80. The methodof claim 65, wherein the bulk gallium and nitrogen containing substrateis grown epitaxially, ammonothermally, by hydride vapor phase-epitaxy,by metalorganic chemical vapor deposition, by molecular beam epitaxy, byliquid phase epitaxy, by a flux method, or by a combination of any ofthe foregoing.
 81. The method of claim 65, wherein the bulk gallium andnitrogen containing substrate comprises at least one regioncharacterized by a surface dislocation density below about 10⁷ cm⁻². 82.The method of claim 65, wherein the light emitting diode is operable ina continuous wave mode.
 83. The method of claim 65, wherein the lightemitting diode is operable in a pulsed mode.
 84. The method of claim 65,wherein the light emitting diode is characterized by a lumens per activejunction area greater than 300 lm/mm², for a warm white emission with acorrelated color temperature (CCT) of less than about 5,000K, and acolor rendering index (CRI) greater than
 75. 85. A method of using alighting fixture, the method comprising: providing a lighting fixturecomprising a light emitting diode, wherein the light emitting diodecomprises: a bulk gallium and nitrogen containing substrate having asurface region; and at least one active region formed overlying thesurface region; a current density from 175 Amps/cm² to 2,000 Amps/cm²characterizing the at least one active region; and wherein the lightemitting diode is characterized by an external quantum efficiency (EQE)of at least 50%, and a peak emission wavelength between about 385 nm andabout 480 nm; and emitting electromagnetic radiation having the peakemission wavelength between about 385 nm and 480 nm.
 86. A method ofusing a lighting fixture, the method comprising: providing a lightingfixture comprising a light emitting diode, the light emitting diodecomprising: a bulk gallium and nitrogen containing substrate comprisinga surface region characterized by a c-plane orientation; one or moren-type epitaxial layers overlying the surface region; at least oneactive region formed overlying the one or more n-type epitaxial layers,wherein the at least one active region comprises one or more activelayers, a current density from 175 Amps/cm² to 2,000 Amps/cm²characterizing the at least one active region; one or more p-typeepitaxial layers overlying the at least one active region; at least onereflective p-type contact overlying the one or more p-type epitaxiallayers and electrically coupled to a first side of the at least oneactive region; and at least one n-type contact electrically coupled to asecond side of the at least one active region; wherein the lightemitting diode is characterized by an external quantum efficiency (EQE)of at least 50%, and a peak emission wavelength between about 385 nm andabout 480 nm; and emitting electromagnetic radiation having the peakemission wavelength between about 385 nm and 480 nm.
 87. A method ofusing a lighting fixture, the method comprising: providing a lightingfixture comprising a light emitting diode, the light emitting diodecomprising: a bulk gallium and nitrogen containing substrate having asurface region characterized by a semipolar orientation; and at leastone active region formed overlying the surface region, a current densityfrom 175 Amps/cm² to 2,000 Amps/cm² characterizing the at least oneactive region; wherein the light emitting diode is characterized by anexternal quantum efficiency (EQE) of at least 50%, and a peak emissionwavelength between about 385 nm and about 480 nm; and emittingelectromagnetic radiation having the peak emission wavelength betweenabout 385 nm and 480 nm.
 88. A method of using a lighting fixture, themethod comprising: providing a lighting fixture comprising a lightemitting diode, the light emitting diode comprising: a bulk gallium andnitrogen containing substrate having a surface region characterized by anonpolar orientation; and at least one active region formed overlyingthe surface region, a current density from 175 Amps/cm² to 2,000Amps/cm² characterizing the at least one active region; wherein thelight emitting diode is characterized by an external quantum efficiency(EQE) of at least 50%, and a peak emission wavelength between about 385nm and about 480 nm; and emitting electromagnetic radiation having thepeak emission wavelength between about 385 nm and 480 nm.
 89. A methodof using a lamp comprising, the method comprising: providing a lampcomprising a light emitting diode, wherein the light emitting diodecomprises: a bulk gallium and nitrogen containing substrate having asurface region; and at least one active region formed overlying thesurface region; a current density from 175 Amps/cm² to 2,000 Amps/cm²characterizing the at least one active region; and wherein the lightemitting diode is characterized by an external quantum efficiency (EQE)of at least 50%, and a peak emission wavelength between about 385 nm andabout 480 nm; and emitting electromagnetic radiation having the peakemission wavelength between about 385 nm and 480 nm.
 90. The method ofclaim 89, wherein the lamp is a replacement lamp.
 91. The method ofclaim 89, wherein the lamp conforms to a form factor selected from anA-lamp, a fluorescent tube, a compact fluorescent lamp (CFL), a metallicreflector (MR) lamp, an MR16 lamp, a parabolic reflector (PAR) lamp, areflector bulb (R), a single end quartz halogen lamp, a double endquartz halogen lamp, a candelabra, a globe bulb, a high bay lamp, atroffer lamp, and a cobra head lamp.
 92. A method of using a lamp, themethod comprising: providing a lamp comprising the light emitting diode,the light emitting diode comprising: a bulk gallium and nitrogencontaining substrate comprising a surface region characterized by ac-plane orientation; one or more n-type epitaxial layers overlying thesurface region; at least one active region formed overlying the one ormore n-type epitaxial layers, wherein the at least one active regioncomprises one or more active layers, a current density from 175 Amps/cm²to 2,000 Amps/cm² characterizing the at least one active region; one ormore p-type epitaxial layers overlying the at least one active region;at least one reflective p-type contact overlying the one or more p-typeepitaxial layers and electrically coupled to a first side of the atleast one active region; and at least one n-type contact electricallycoupled to a second side of the at least one active region; wherein thelight emitting diode is characterized by an external quantum efficiency(EQE) of at least 50%, and a peak emission wavelength between about 385nm and about 480 nm; and emitting electromagnetic radiation having thepeak emission wavelength between about 385 nm and 480 nm.
 93. The methodof claim 92, wherein the lamp is a replacement lamp.
 94. The method ofclaim 92, wherein the lamp conforms to a form factor selected from anA-lamp, a fluorescent tube, a compact fluorescent lamp (CFL), a metallicreflector (MR) lamp, an MR16 lamp, a parabolic reflector (PAR) lamp, areflector bulb (R), a single end quartz halogen lamp, a double endquartz halogen lamp, a candelabra, a globe bulb, a high bay lamp, atroffer lamp, and a cobra head lamp.
 95. A method using a lampcomprising a light emitting diode, the method comprising: providing alamp comprising a light emitting diode, the light emitting diodecomprising: a bulk gallium and nitrogen containing substrate having asurface region characterized by a semipolar orientation; and at leastone active region formed overlying the surface region, a current densityfrom 175 Amps/cm² to 2,000 Amps/cm² characterizing the at least oneactive region; wherein the light emitting diode is characterized by anexternal quantum efficiency (EQE) of at least 50%, and a peak emissionwavelength between about 385 nm and about 480 nm; and emittingelectromagnetic radiation having the peak emission wavelength betweenabout 385 nm and 480 nm.
 96. The method of claim 95, wherein the lamp isa replacement lamp.
 97. The method of claim 95, wherein the lampconforms to a form factor selected from an A-lamp, a fluorescent tube, acompact fluorescent lamp (CFL), a metallic reflector (MR) lamp, an MR16lamp, a parabolic reflector (PAR) lamp, a reflector bulb (R), a singleend quartz halogen lamp, a double end quartz halogen lamp, a candelabra,a globe bulb, a high bay lamp, a troffer lamp, and a cobra head lamp.98. A method of using a lamp, the method comprising: providing a lampcomprising a light emitting diode, the light emitting diode comprising:a bulk gallium and nitrogen containing substrate having a surface regioncharacterized by a nonpolar orientation; and at least one active regionformed overlying the surface region, a current density from 175 Amps/cm²to 2,000 Amps/cm² characterizing the at least one active region; whereinthe light emitting diode is characterized by an external quantumefficiency (EQE) of at least 50%, and a peak emission wavelength betweenabout 385 nm and about 480 nm; and emitting electromagnetic radiationhaving the peak emission wavelength between about 385 nm and 480 nm. 99.The method of claim 98, wherein the lamp is a replacement lamp.
 100. Themethod of claim 98, wherein the lamp conforms to a form factor selectedfrom an A-lamp, a fluorescent tube, a compact fluorescent lamp (CFL), ametallic reflector (MR) lamp, an MR16 lamp, a parabolic reflector (PAR)lamp, a reflector bulb (R), a single end quartz halogen lamp, a doubleend quartz halogen lamp, a candelabra, a globe bulb, a high bay lamp, atroffer lamp, and a cobra head lamp.
 101. A method of using a lamp,wherein the lamp conforms to a MR16 form factor and comprises a lightemitting diode, the method comprising: providing the lamp conforming toa MR16 form factor and comprising a light emitting diode, the lightemitting diode comprising: a bulk gallium and nitrogen containingsubstrate having a surface region characterized by a c-planeorientation; at least one active region formed overlying the surfaceregion, a current density from 175 Amps/cm² to 2,000 Amps/cm²characterizing the at least one active region; and at least one phosphoroperably coupled to the at least one active region to produce a whitelight emission; wherein the light emitting diode is characterized by anexternal quantum efficiency (EQE) of at least 50%, and a peak emissionwavelength between about 385 nm and about 480 nm; and emittingelectromagnetic radiation having the peak emission wavelength betweenabout 385 nm and 480 nm.
 102. The method of claim 101, wherein thecurrent density is from 400 Amps/cm² to 800 Amps/cm².
 103. The method ofclaim 101, wherein the current density is from 200 Amps/cm² to 1,000Amps/cm².
 104. The method of claim 101, wherein the current density isfrom 500 Amps/cm² to 1,000 Amps/cm².
 105. The method of claim 101,wherein the current density is from 1,000 Amps/cm² to 2,000 Amps/cm².106. The method of claim 101, wherein the light emitting diode ischaracterized by a lumens per active junction area of greater than 300lm/mm², for a warm white emission with a correlated color temperature(CCT) of less than about 5,000K, and a color rendering index (CRI)greater than 75.